When designing or specifying cabinets and enclosures, hinges play a key role in determining whether or not the product lives up to expectations. With literally thousands of products on the market, there’s usually a standard one that fits the bill and is available for quick delivery. But all those choices can make the selection process a bit overwhelming. Here are several basic points engineers should consider to help zero in on the hinge best suited for a particular enclosure.
Who, What, Where
Authored by Jim Ford
Product Manager, Hinges and Positioning Technology,
Edited by Kenneth J. Korane,
• Thousands of standard hinges are available for quick delivery.
• Nailing performance specs early in the design keeps expenses down and prevents costly redesign or the need for special hardware.
Southco Inc., southco.com
Consider the specs
To minimize total product costs and maximize performance and life, engineers need to identify the critical performance parameters early in the design process. Considerations such as applicable industry standards (NEMA or IP sealing), load requirements, environmental conditions, and aesthetics all affect hardware selection and enclosure design.
For instance, appearance concerns can make concealed hinges preferable to exposed ones. Internal or external space constraints also affect designs. The product environment and corrosion-resistance requirements, often expressed in terms of hours of salt-spray exposure per ASTM B-117, can drive material and finish selection.
Electromagnetic interference (EMI) shielding requirements are typically defined as the degree of attenuation at a specified frequency. To determine actual performance, hinges for EMI-shielding applications must be evaluated as part of the complete enclosure. Note that hinges mounted outside the sealed area do not affect performance.
Other factors such as environmental sealing, material preferences, and flammability ratings can all influence hinge selection. Fortunately, hardware comes in steel, stainless steel, die-cast zinc, brass, various plastic blends, and many other materials. There are also a range of platings and coatings to suit most any environmental concern.
And planning ahead often means the difference between meeting cost and delivery goals and facing unwanted budget overruns and expensive delays. For example, when enclosures require concealed hinges, minor — but significant — changes to the door and frame in the early stages of design can allow the use of standard products. Deciding on concealed hinges late in the game, however, often means costly redesign or the need for custom hinges.
Fixed versus removable
Next consider the physical hinge style that meets your primary performance characteristics. For enclosures that need only a basic open/shut design, consider free-operating, fixed-mounted hinges. These are typically the simplest, most economical products for attaching doors to enclosures, provided a permanently attached, fixed hinge offers acceptable door swing space and life.
Designers should also consider removable door hinges. Two-piece door-removal hinges let users completely detach the door for maximum access and flexibility in design and operation. This style of hinge is valuable when enclosures are shipped disassembled, where the door panel ships from a different location than the main enclosure body, or if the enclosure door must be removed to allow unimpeded access for equipment upgrades, service, or routine maintenance.
Visible lift-off style door-removal hinges provide the easiest approach. They mount on the enclosure exterior, and users simply unlatch the door and lift it off pins that stay attached to the frame. Spring-loaded concealed door-removal hinges mount inside the enclosure, for more security and cleaner appearance. With the door open, users retract the hinge pins to release the door.
Lift-off hinges let workers keep both hands free while handling the door. Retractable- pin hinges can be used in close quarters if there is not enough room to lift and manipulate the door.
In or out
Internally and externally mounted hinges each have specific design considerations and advantages, and their selection could ultimately depend on the existing door frame.
Internally mounted hardware satisfies concerns about appearance and minimizes vandalism opportunities. Typically they require more space inside, which can be a problem in small, tightly packed enclosures.
Externally mounted hardware offers greater overall strength, more universal fit, greater flexibility for removable hinges, and is easier to specify later in the design cycle.
Sometimes free-swinging enclosure doors can be a nuisance or hazard. Hinge-based positioning devices can hold doors open at various predetermined positions without the need for additional space-consuming hardware such as gas struts or door stays. These can be particularly valuable in horizontally hinged applications like compartment lids and flip-up access doors, or outdoors where wind can blow doors closed. Several types are available.
Detent hinges provide a mechanism to engage the door at one or more predetermined angles within its range of motion, ensuring the door will stay open at a specific angle. Some horizontally mounted hinges let a door swing down to form a shelf, or swing up to hold the door open.
Constant-torque hinges maintain consistent resistance throughout the full range of motion, giving users infinite position control. Some hinges have a preset torque resistance. Others let users adjust torque and adapt one type of hinge to a range of door loads, or permit more restrictive or liberal door swing. Other positioncontrol styles include self-closing hinges and hinges with built-in dampening.
Designers should always specify hinges to accommodate not only the basic door weight, but also the maximum anticipated load on the door — which can change depending on where and how an enclosure gets used. For example, increasing the door’s width-height ratio increases the stress on hinges. And depending on the application, consider external forces that may be applied by workers who step, lean, hang, or pull on a door.
If weighing the door is not an option, calculate it by height width depth density of the door material. CAD software can also accurately determine door weight and center of gravity.
To select appropriate hinges, especially in larger door installations, determine both the maximum load and center of gravity (cg). The maximum force on the hinge can be determined by combining all external loads and the reaction forces generated by gravity acting on the cg of the door.
Manufacturers’ catalog data typically lists hinge strength guidelines, such as maximum axial and radial static load capacities, and ultimate axial and radial loads. In addition, mount the hinges as far apart as possible along the longest edge of a door to maximize strength. Closer, more-even hinge spacing helps maintain rigidity, reduce door flexing, and ensure more-even gasket sealing.
Taking into account these guidelines gives a better understanding of the criteria required to specify enclosure hinges. Engineers can also seek design help from manufacturers that offer a wide range of hinge options to meet specific needs. Partnering with a knowledgeable, experienced supplier typically gives access to a broader range of information, advice, and options.